Pressure: when is too much and why?

[Tell]

I’ve been reloading for less than two years. I spent a lot of time reading on a bunch of different forums, and watched a lot of videos. I don’t know why this seems like a hard thing to pin down, but I can’t quite figure out how much pressure is too much. And most importantly - why. It seems like the first thing we’d all want to know. I know signs, and I know I’ve been over pressure, but I’d like to know what happens in what order, and what the danger is. Yes, I know death and dismemberment are the dangers, but I’d like to know specifically how and why.

I’ve fired decent amount of rounds that have ejector marks, and I hear guys talk about velocities that are too high and then they say they’re running hot, but they don’t seem to be worried about it. Even Jake from unknown says he’ll load stuff super hot because he doesn’t care how many firings he gets out of the brass, and he knows the action can take it. On the other hand, some guys are extremely wary of getting velocities over book max.

I don’t mind if I only get a few firings out of brass, but I want to know what the real danger is in order of likelihood as pressure increases. I know of case head separation, but I don’t really know what else would happen before that. And I’d really like to know what the dangers are.

Thanks in advance. I know there are a lot of incredibly knowledgeable reloaders on this forum.

 

[Wrench]

I know of two savages that launched extractors. When you consider the path out of the rifle....it should make you nervous.

We all pays our money and takes our chances. Unless you're trying to make PF or are sponsored by a brass company, the benefits of an extra few fps isn't anything that can't be overcome with a couple of clicks.

 

[Tell]

Thanks Wrench. I’d like to know if, in those two cases, was there heavy bolt lift and pretty flat primers, and then one day it blew the extractor? Or was he piercing primers and had some other sort of issue but shot anyways? And if you pierce a primer, does that mean you’re going to get something in the face?

I’m not saying I want to run the ragged edge. I just would like to know why some people are a lot less worried about it and are willing to run top of the line brass so hard that they can’t get two firings out of it because the pocket is too loose.

 

[Wrench]

Piercing doesn't mean you're going to get hit in the face....but it certainly make it a possibility. What piercing can do is lock up triggers, chew up bolts and make more pierced primers easier due to pin hole erosion.

On the savage extractors, one was obviously running hot, the other was not but was fired with the muzzle on hair.

 

[jfk69]

I don’t care how strong someone “thinks” an action is and what they “think” it can handle. All I “think” about is 60k psi going off 6 inches from my face. I don’t feel the need to risk my ugly mug for a few clicks of elevation several hundred yards down range.

 

[Lawnboi]

The real problem happens when you touch one off in the rain, or snow and have some moisture on the round/chamber.

I load low because of that. If I want more speed I’ll move to a bigger case.

 

[B_Reynolds_AK]

@2y2c

This is a very good question and something that I’d like to hear more about as well. Besides for the ‘launched extractors’, even the replies so far are not answering your questions. You almost always just hear, add a couple clicks or watch for heavy bolt lift etc, but none of those things answer the questions as posed. I hope there is some good discussion that continues here that addresses those in more depth.

 

[Wrench]

The real answer is pay attention to your velocity. If you should be maxing out at 2800 but the chronograph or corrections tell you that you are in the 3k area.....how do you think that happened? Furthermore, accuracy is almost always worse as you reach the peak.

Lastly, some powders (re26) do a great job of not showing pressure while exceeding expected velocity. These powders go from hero to flat out scary with a conditions change. I've had the same box, loaded on the same day with the same lot # of components go from no signs to literally blowing primers out of the pockets and swelling the head.

I used to push 26 as the miracle powder, now I tell people to stay away....the spike is dangerous.

 

[pbroski]

There is a direct correlation between velocity and chamber pressure. If your velocity is higher than what the load data shows, it's that way because of pressure. Download Gordon's Reloading Tool or buy QuickLoad and play around with the powder charge numbers. You'll see that the loads some people use will exceed 80000 psi. This is confirmed by tests that Hornady have done.

Heavy bolt lift, extractor marks, flattened primers, etc. may not show until the pressures are way above saami pressure specs for the cartridge. A better way is with the use of a chrono. Stop adding powder when the gun gets the velocity it should.

 

[JGRaider]

I've never experienced those problems with RL26 personally. Interesting. What's not interesting is this "Jake from unkown" that knowingly produces these "super hot" loads. That guy's an idiot.

 

[A382DWDZQ]

When is too much and why? For me, I feel that for most of what I reload, i just try and stay about 1,500 psi under SAAMI max avg pressure. Lately, I don’t seek out max. Instead I have been more focused on reduced or minimum recoil. I don’t have a problem using a load that is running low end or middle if it shoots well.

That said, I have worked up loads to find “pressure”. It was definitely something I had to learn. Between using QuickLoad, published load data, pressure signs, experience, data from prior shooting, and a chronograph, I feel like I can pretty accurately tell what psi a load is at give or take maybe 500-1000.

I don’t feel comfortable with hot loads, those that are over published SAAMI pressure. I guess I would say I’m ok with staying within the industry standards and their determination of what is safe. Why and what order things fail can vary and depends on a lot of different factors. A lot of those I do not know. For example, I don’t know the specifics of the metal used to build my actions and I don’t know the engineering specifics of them. So I don’t have the information to predict the maximums they will withstand, just that they are safe to industry standards. I have read that bolt action rifles are made so that the barrel will fail before the action in order to protect the shooter. Does that mean they all will fail like that? Certainly not.

When it comes to people who load within the safety factor margin, meaning above the industry max pressure for a cartridge but below where the gun blows up, I would guess it is not so much that they are not worried about certain things as much as it is that they have a lot more knowledge and experience to inform their risk. They probably know the components and the variables a lot better than most and they can more accurately control those variables. Then again, some might just be more tolerant to higher risk.

Pressure is measurable and the factors that cause firearms to fail are as well. There are many many variables, so for myself, I learn the signs that tell me when I am exceeding the average maximum pressure, and when I work up a load I estimate and analyze where I think the pressure is at, in PSI. If I go over, I reduce the pressure. I know that the body of knowledge is vast and learning more is one of the things I enjoy about this.

 

[JGRaider]

Wondering how you are measuring pressure? Thanks.

 

[Vern400]

Say your rifle is designed for 62,000 PSI.
Suppose your brass is almost okay to 80,000 PSI
Suppose you're primers are good for 80,000 PSI.
This is hypothetical, but the numbers are probably reasonable.

THEN
Your friend comes over, and you decide to set out 50 milk jugs arranged randomly from 50 to 500 yd. He who hits most wins. You fire 30 shots in 2 minutes. You declare victory! But your friend says no, there's one remaining behind a clump of grass.

So, you loaded to 70,000 on a 50 degree day. But your round cooked in a 160 degree barrel for 2 minutes. And you fire the last shot.

Maybe you were using Varget which is somewhat temperature tolerant and everything holds together. But maybe you were using RL15.

That's the why. Thank God my rifle held together. It took a lot of work to open the bolt and dig out the top half of the case. I took the rifle to a good gunsmith and had it checked out. Then I had to pull 300 bullets. It was a 308.

Today, I stop at published velocity, or when the first signs of primer distress show up, whichever happens first. And I'll go through 10 or 20 rounds on a very hot day just to make sure.

I won't hesitate to go to Max charge if that's what shoots best. But if I need that extra hundred feet per second, I should get more gun.

I could make this crap up. But I didn't.

The picture of included was from my next door neighbor who somehow loaded a 300 blackout in the middle of a 556 mag. No idea how it happened because he didn't have a 300 blackout. He got to enjoy some emergency surgery on his right hand and arm. Whether it's a bolt gun or a gas gun the result ain't good.

That's the best answer I can give you, chief!

 

[Wrench]

Problems arise from tolerance stacking. A tightly bushed firing pin will take a lot more to pierce a primer than some cratered out POS.

EVERYONE talks about prefits and thinks stuffing a gauge on a barrel nut makes them a rifle builder......how many have measured bolt nose clearance?

Brass can take a lot when it's fully supported. Throw a fat gap on the bolt nose clearance and suddenly things can get scary.

 

[A382DWDZQ]

Wondering how you are measuring pressure? Thanks.

I am just extrapolating based on different data points from published data and QuickLoad. I match my charge and velocity to what QuickLoad calculates and to what the published load data is. I don’t have a way to measure my actual pressure, but based on this, it seems to track pretty close. It correlates to when I get noticeable pressure signs as well. So if my velocities for a load are matching what I have in QuickLoad, I usually assume that the pressure is close to that also.

 

[Warmsy]

The real problem happens when you touch one off in the rain, or snow and have some moisture on the round/chamber.

I load low because of that. If I want more speed I’ll move to a bigger case.

Is there any risk with factory ammo in 30 06? I often hunt in the rain, but have never fired a shot in those conditions. My rifle will often be soaked. Is that dangerous?

 

[TaperPin]

The only reason we have the discussion about pressures is that we want loads that are safe and reliable - no?

For any combination of components in a modern bolt action the weak links In the chain are primers and brass - the rifle itself will handle far more pressure than the brass or primer will.

Blanking a primer can put the gun out of commission, so avoid pressures high enough to blank a primer.

Sticking a case in the chamber or having a case head separation can put you out of commission - avoid those pressures.

If a case can be loaded 10x without even a partial head separation, doesn’t expand primer pockets, doesn’t stick, and doesn’t blank primers I consider it safe and reliable. If a case only survives 5 reloads before thinning enough to have a head separation, that may work, but it is at much higher chance of causing a problem, so I back off a little.

There are rifles that cannot fire a published max load for even a couple of reloads - there is no way that pressure is less than another gun that uses a slightly over published max load and gets 10 reloads.

What gets people in trouble is not appreciating how easy it is to take a max load, change a single component, and then be over max. Or they let a cartridge cook in a 200 degree chamber and wonder why the primer just falls out, or they have to hammer the bolt to get it to open. What’s printed in a book or computer program will be close, but it’s not exact.

I measure case head diameter before and after firing, check case head thinning with a paper clip, count the number of times a case can be loaded to failure, keep an eye out for primer signs, and expect some ejector marks. I’ve never had to hammer open a bolt, or blanked a primer, or had a rifle become incapacitated.

 

[Bluefish]

What happens when pressure is too high? Provided your brass or primers doesn’t fail as a pressure relief, the steel may fail eventually in the rifle. Could be barrel, could be on the bolt. Also steel has a force vs number of cycles curve that has a knee. Big enough force and you dont even get one cycle. Keep it low enough and you get infinite cycles. We like to stay below that knee. this can be seen in AR bolt failures with larger bolt faces. The bolt becomes a wear item. Replace it every so many cycles or it may fail. problem with overloading, you don’t know that pressure vs cycle curve and you don’t know when it might fail.
it also depends on design. Some rifles are overbuilt and probably won’t ever fail. You will just destroy brass. Others may be marginal at factory loads and won’t hold up to more than a few hot loads. Look at 45-70 loadings. There are 3 different pressure levels depending on the action. Put a ruger #1 load in a trapdoor Springfield and it will break. Yet the brass holds up fine.

fatigue life is probably not much of an issue for barrels in rifles as we don’t go that many rounds before replacing them. Shotguns are a different story. Some guns may go several 100k, thus fatigue failure could be an issue. Might be an issue with a rifle bolt with a lot of hot rounds.

 

[Lawnboi]

Is there any risk with factory ammo in 30 06? I often hunt in the rain, but have never fired a shot in those conditions. My rifle will often be soaked. Is that dangerous?

Factory ammo is pressure tested and likely safe in that situation.

Personally I water test my ammo. Along with heat. I don’t want to find out I’m not getting my bolt open after a shot when I’m hunting or at a match. This is not something I’d tell everyone to do though.

 

[Tmac]

If you are looking for a safe point to stop, I’d suggest stopping at the book charge max or book velocity max, what ever you hit first. Even better, consult multiple sources and stop a grain or so or 40-50 ish fps under max. . You can be over pressure and not see obvious signs on the brass, some signs are not visible to most of us and may take a caliper to “see”. Many can and do go past max’s and not have issues, but many eventually do have issues. Personal choice.